This invention relates to gas turbine engines and, more particularly, to apparatus for maintaining minimum clearance between variable position airfoils and the walls forming the gas flow path associated with the engine.
It is well known in the gas turbine engine field that the performance of the engine over its cycle may be improved by utilizing variable position airfoils within various portions of the engine. By way of example, some modern day engines utilize variable stator vanes in the compressor section of the engine which typically rotate between a relatively closed position under low power conditions and a fully opened position under full power conditions. Other applications of variable position airfoils include variable position fan blades in high bypass gas turbine engines and variable inlet guide vanes and variable position turbine blades and vanes.
It is also well known that clearances between the ends of the airfoil and the walls of the flow passage have an adverse effect upon engine performance. Larger clearances cause greater losses in performance. With variable position airfoils the losses are accentuated due to the rotation of the airfoil. More specifically, the clearance between the ends of the airfoil and the adjacent aerodynamic flow path surfaces varies in accordance with the position of the vane. This result obtains from the inherent mismatch between the flow path contour which is a curved surface of revolution, and the radially facing inner and outer surfaces of the airfoil which travel in a flat plane as the airfoil is rotated. Heretofore, designers have avoided interference of the airfoil edges and the walls of the airfoil by machining away portions of the edges of the airfoil which would otherwise interfer with the flow path walls when the airfoil is disposed in the extreme closed or opened position. This technique, while assuring minimum clearances when the airfoil occupies the one position, results in large clearances when the airfoil is disposed in other rotational positions. Often large clearances occur at critical high operating time power settings and vane positions causing increased air leakage, engine performance loss and greater fuel consumption. This invention addresses the aforementioned problem relating to excessive clearances associated with variable position airfoils.
Therefore, it is an object of the present invention to provide for minimum clearances between the edges of a variable position airfoil and the walls defining the engine flow path in all rotational positions of the airfoil.
It is another object of the present invention to eliminate variations in clearance as the variable position airfoil is rotated.